(a) Field of the Invention
The present invention relates generally to a liquid crystal display and, more particularly, to a liquid crystal display including a sensing unit.
(b) Description of the Related Art
Liquid crystal displays (LCDs) typically include a pair of panels that are provided with pixel electrodes and a common electrode, as well as a liquid crystal layer with dielectric anisotropy interposed between the two panels. The pixel electrodes are usually arranged in a matrix pattern and are connected to switching elements, such as thin film transistors (TFTs), such that they receive image data voltages row by row. The common electrode covers the entire surface of one of the two panels and it is supplied with a common voltage. A pixel electrode and corresponding portions of the common electrode and corresponding portions of the liquid crystal layer form a liquid crystal capacitor that, along with a switching element connected thereto, is a basic element of a pixel.
An LCD generates electric fields by applying voltages to pixel electrodes and a common electrode, and the strength of the electric fields applied thereto are varied in order to adjust the transmittance of light passing through a liquid crystal layer, thereby displaying images.
Touch screen panels write or draw letters or pictures by touching a finger, touch pen, or a stylus to a display panel or carry out desired operations of machines such as computers, etc. by operating icons. LCDs attached to the touch screen panels determine whether contact is made with the display panel (e.g., via a finger, the touch pen, etc.) and, if so, a corresponding touch position. While these panels provide certain advantages, the manufacturing costs of the LCDs that incorporate touch screen panels increase as compared to the costs of LCDs that do not employ touch screen panels. Furthermore, the process used in attaching the touch screen panel to the LCD causes a reduction in the yield and the luminance of the LCD, as well as an increase in the thickness of the LCD.
For solving the above problems, a plurality of photo sensing units, which are implemented with thin film transistors, may be integrated into pixels displaying images of the LCD. The photo sensing unit senses the variation of light incident upon the display panel by a touch of the finger or an implement of a user, to determine whether there has been contact with the display panel and a touch position. However, these photo sensing units influence characteristics such as intensity of external light, intensity of light from a back light unit included in the LCD, and temperature, thereby resulting in a decrease in the accuracy of a corresponding sensing operation.